The present invention relates to a process and apparatus fo machining an electrode workpiece by means of an electrode tool, wherein successive voltage pulses are applied across the electrodes for triggering machining electrical discharges, the voltage pulses being obtained by connecting across the electrodes a DC source after a first predetermined time interval following the end of an electrical discharge and disconnecting the source from across the electrodes after at least a second predetermined time interval following the beginning of an electrical discharge.
Pulse generators operating as indicated above are well known in EDM technology, and they are able to provide each voltage pulse with a predetermined duration from the moment at which a machining electrical discharge begins. Under such circumstances, the duration of each pulse is controlled independently of the delay time interval between the voltage pulse and the current pulse. It has been observed that when electrical discharges occur in the machining zone between the electrodes during an EDM operation, bridging of the electrodes by metallic particles may repeatedly be formed, thus causing short circuits between the electrodes and non-machining electrical discharges, especially during finish machining.
Because such short circuits not only decrease the machining efficiency, but they tend to degenerate into electrical arcs whose principal effect it is to damage the machined surfaces and the electrode tool, diverse methods have been developed in the past to eliminate the short circuits between the electrodes. However, it has been observed that, in the majority of cases, the metallic bridges between the electrodes are weak enough to spontaneously disppear by melting away as the result of the passage therethrough of a short circuit current during a single pulse and, therefore, the effective machining characteristics of the electrical discharge is reestablished in the course of that single pulse.
When machining is effected by means of conventional pulse generators as briefly described hereinbefore, and when a short circuit spontaneously disappears during a single pulse, the duration of the effective machining segment of the electrical discharge is considerably reduced and can even be nil when the short circuit disappears simultaneously with the end of the pulse. It is therefore necessary to wait uselessly until the beginning of the following pulse to trigger a new effective electrical discharge.